Here is dual svs sb3000 in my room, which is 28’ long by 17’ wide and 9’ tall. Also opens up to other rooms as well like a kitchen and great room. I did a list of the subs I had all at that time. Was dual Rythmik fv18pc, dual monolith 15, dual svs sb3000 and the last one says Logan which is my sons room that he wanted to see how his compares. His room is dual energy exl12 ported subs, nicer 20 years ago.
One sb3000 in your room should have way more output than a pb1000. Maybe it could be close from 15-30 hz but I’d be surprised. Try running audyssey again, and also try running rew if you can. Time align your subs correctly and don’t rely on audyssey. I’ve run audyssey and then run rew to see 100-105db flat output. I was very disappointed until I ran rew and started playing with distance and unlocked around 10db more of output.